Organic Rankine cycles are typically used in megawatt-scale power plants, where power production and equipment are monitored at all times by human staff. At such plants, a specified turbine inlet pressure is necessary to maintain efficient operation. Constant heat input and output temperatures help maintain efficiency at the rated output. To compensate for periods of reduced or no solar insolation, one or more auxiliary heat source(s) may be utilized to maintain a constant heat input. Efficient heat rejection, and therefore, efficient operation of such plants, usually requires a near-constant low-temperature reservoir, for example a large body of water that has a temperature that does not vary significantly throughout the year.
These conditions, which help ensure efficient operation of all the components of the thermodynamic engine, generally can not be met in small power plant installations desired by and beneficial to remote communities lacking a traditional energy grid. First, employing a full-time staff member is rarely economically feasible, relative to the cost of the technology; therefore, an autonomous installation is desirable. Second, a collection and conversion cycle that can function efficiently with a variable hot side temperature would be desirable, as it would mitigate the variability attendant with using the sun as an energy source, while diminishing or eliminating the need for a supplemental heat source or an independent heat storage system. Third, rural and distributed installations are not necessarily located near an expendable cold water source; this is particularly true in areas with high solar insolation, which are likely to be arid. In such cases, it would be beneficial to have a system that can reject waste heat to the surrounding air. As the ambient air temperature fluctuates during the day and year, the ideal system would adjust its operation to maintain efficient power conversion. Last, the material cost of a solar collection and conversion system can often be prohibitive in economically disadvantaged communities; thus, a solar collection system that is made from inexpensive, readily available parts would also be desirable.
Accordingly, there is a need to provide systems and methods for collecting and converting solar energy into other forms of energy, in particular mechanical and electrical energy. Additionally, these systems should function on a small scale, and in a technically and economically feasible way.